The natural choice would be to use the Teleport power and add certain modifiers to it, but the way the Portal Gun works it isn't exactly like teleport.

Right now I've come up with the following modifiers, but I'm not sure what to value them at:

1. You can't teleport to somewhere you can't see, or into a closed room. I'd probably price this modifier at -1.

2. Each end of the portal must be placed on a solid, immobile surface. This would likely be another -1.

3. The portals can stay open indefinitely, allowing anyone to pass through, so Fatigue for taking others along is not a factor at all. You can also use it against unwilling targets by just putting a portal underneath them. This eliminates a few major limiting factors of the Teleport power, so this should be fairly expensive, at least +8.

4. Accurate placement of the portals requires a Shooting roll, with a range of 3/6/12 (modified upward relative to the 'Extra Range' modifier). I'd probably price this at-2.

This brings the price of Teleport to 7 (3 -1 -1 +8 -2), or 5 as a device.

Any other suggestions?_________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

It takes 2 portal ends to teleport. Since the gun should have a ROF of 1, successful teleportation during combat takes two rounds (since you can't do the same action twice).

I would put the range of the teleportation as "infinite", given the use of the gun at the end of the second movie. This of course requires the person to forgo any other teleportation while leaving the far end open.

Good point. If I'm going to allow him to use the gun against others, it would need to have an ROF of 2. I can add that modifier from the Ranged Attack power._________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

I think you are underestimating the value of portals that can stay open indefinitely, allowing anyone to pass through, and can be used against unwilling targets by just putting a portal underneath them.

Teleport Others, for example, is a +5 modifier to Teleport and allows the teleporter to teleport others "to them" and requires a Spirit roll to succeed (which is opposed if the target is hostile), and incurs multi-action penalties to teleport multiple targets.

From what I understand, you've proposed a +8 modifier to Teleport that allows the teleporter to teleport others:
1. anywhere, but only between two preset locations at a time,
2. without any chance of failure (except a shooting roll) and removes all negative consequences of failure,
3. regardless whether the target is willing,
4. creating a potentially permanent "path",
5. others may use on their turns,
6. and does not require any further action other than a Move action to use after the two locations have been preset.

Compare also to Matter Control, which would permit the character to create a bridge/tunnel between two locations (somewhat similar) which would be semi-permanent, requiring no further action and could subsequently be used by anyone else. 10,000 lbs. per level of steel at range 24" (which is 48 meters).
I don't really know how much a steel bridge would weigh, but the Steel Bridge in Portland is 64m long and has counterweights to raise the bridge deck for ships which weigh 9,000,000 tons (thanks wiki!). The power permits a Medium burst template per level which, if my math is correct, is 12.5 square game inches area covered by a few real-world inches of steel, so a 4" bridge per level? or 12"?
This would also not permit as many options as the Portal gun, but our hero could still create a "slide" under their opponents that would dump them off the side of the building to fall to their death.

Consider also the potential of the Portal Gun to permit a character to travel at Speeds in excess of Flight.
Also, doesn't the Portal Gun only work on specially designed surfaces?

You make some good points. Not requiring an opposed Spirit roll is at least partially mitigated by the need for a successful Shooting roll to get the portals exactly where you want them.

As for template size, judging from what I've seen in the game (and I've never actually played it) the portals would cover a Small burst template at most, and even that's a bit big.

The range I am not backing down on, as I'm not willing to give any modifier for unlimited range teleportation. If the player wants longer range, he needs to buy it in 12" increments as for the Teleport power. I'm not aiming to actually recreating the gun from the game 100% accurately, I'm just modifying the Teleport power to sort of work like that.

What modifiers would you suggest for the power?_________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

Compare also to Matter Control, which would permit the character to create a bridge/tunnel between two locations (somewhat similar) which would be semi-permanent, requiring no further action and could subsequently be used by anyone else. 10,000 lbs. per level of steel at range 24" (which is 48 meters).
I don't really know how much a steel bridge would weigh, but the Steel Bridge in Portland is 64m long and has counterweights to raise the bridge deck for ships which weigh 9,000,000 tons (thanks wiki!). The power permits a Medium burst template per level which, if my math is correct, is 12.5 square game inches area covered by a few real-world inches of steel, so a 4" bridge per level? or 12"?
This would also not permit as many options as the Portal gun, but our hero could still create a "slide" under their opponents that would dump them off the side of the building to fall to their death.

Re-trapping Matter Control isn't a bad idea. I don't have access to my book at the moment, but this is certainly worth looking into. Thanks!_________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

To me it really depends upon the limits.
Will you permit me to put a hole in the ceiling above the target and in the floor below the target, let the target fall for 6 seconds accelerating to 58 m/s and then remove the hole below the target causing a 35d6 damage impact at a speed of 176" per turn or 10d6 for falling 176m?

Questions related to range and line of sight limits:
1. How about creating and keeping one Portal outside the top of a skyscraper and then dropping bad guys out of it in every combat no matter where the combat occurs?
2. How about putting a Portal inside an iron box, closing the box and then teleporting people into the box?
3. What happens to a Portal once I move into another room and cannot see it anymore?

Questions related to duration:
1. How long will a Portal remain open?
2. What happens if it closes while someone is halfway between?
3. Can I put people halfway between and then close it on purpose?

Questions related to size and type:
1. Can I put objects through my Portals or only people?
2. Can I put a piano on a Portal and then put another portal in the ceiling above my opponent causing the piano to fall on them?
3. How about a bathtub full of acid?
4. How about a box of explosives triggered by impact?

I'd add 5 for Teleport Other, add 4 for one level of Matter Control: worm holes to make the Portals semi-permanent and 2 for creating worm holes to for Matter Control, eliminating Spirit and Vigor rolls of Teleport, and not permitting Distraction or other Matter Control uses. I'd rule the device cannot be moved more than 24" from any Portal (and maybe line of sight), require one Action to open one Portal (but allow Rapid Teleport to change this and closing a Portal is free), and use Shooting (+2 for non-moving target) to place the Portal, which must be placed on a solid surface (I'd not limit to immobile surfaces because the world is spinning through space and the 24" limit fixes that). I'd make each Portal a Small Template. (+2 to permit Medium Template). I'd increase the range to 6/12/24 with a 12" maximum unless greater range Teleport is purchased. I'd rule the Portal won't close with an object inside. I'd rule if there is an object in the Portal, and the device is moved more than 24" away from any Portal, the device breaks and must be repaired.

So what is that: 5+2+4 = 11 - 2 (device) = 9. I guess not as much different as I thought it would be, but I think I've limited most of my concerns about significantly powerful uses. However, my players always surprise me, anyway.

Ok, instead of trying to force the one Teleport power to do everything a Portal Gun can do, how's this?

Basic portal travel. You put a portal in one place and the other end at the limit of your range and instantly move between those two points. Trying to carry too much biomass (i.e. taking extra people along) can overload the device, which is why you can still get fatigue from taking others.
— 6 pts. Teleport (3 points +2 for taxi +5 for teleport others −1 for losing the ability to teleport somewhere you can’t see −1 for requiring walls and ceilings −2 for device)

Dealing damage by ‘portaling’ an object into an opponent. You put a portal beneath a heavy object and the other end on a wall beside your opponent; object falls through the portal and hits your opponent.
— 2 pts. Attack, Ranged, up to 3d6 damage (3 points +3 points for extra d6 damage −2 points for requiring material −1 for requiring a wall within range of your opponent −1 point for device)

Trapping a person in an endless fall. You put a portal on the floor under an opponent and the other on the ceiling above them. They fall forever unless you stop them or they are able to grab the edge of the portal to pull free. A person can use Strength (to stop their descent with brute force) or Agility (to catch an edge and roll out of it) to escape as per the normal Ensnare rules.
— 3 pts. Ensnare (3 points +2 for ranged attack −1 for requiring a ceiling above your opponent −1 for device)

Combine them all into a single 11-point device.

I don't want to re-write the rules of the powers in the SPC, so I'm ok with the fact that this portal gun might not work exactly as the one in the game and doesn't have nearly the same kind of range. This is supposed to be a steampunk version for the Kerberos Club setting anyway, so maybe it's just a very early prototype that doesn't work nearly as well as the finished product._________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

You can use it on yourself, you can use it on others, you can use it to throw objects at opponents... it does a lot of what a portal gun does. All you have to do is be a little creative with the trappings. Instead of levitating a person to move them with mind over matter, you use your portal gun to move them with portals. The "weight" limit of the TK is just indicative of the size of the portals themselves: some objects might just be too big to fit through the portal. Change the opposed Spirit to opposed Agility rolls when trying to move an unwilling target._________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!

12 pts. for a Portal Gun Device that can move up to 1,000 lbs. at a range of 24", and can capture someone in a never-ending fall which is very difficult to escape from.

One might also create modifiers for the "requires a solid, immobile surface", but for just the basics, that seems to work pretty well._________________'But I don't want to go among mad people,' Alice remarked.
'Oh, you can't help that,' said the Cat: 'we're all mad here.'
The Order of the Dice... OF DOOM!